1. Field of the Invention
This invention is related to electronic measurement devices, and more particularly to electrostatic discharge event detectors.
2. Background Art
Electrostatic discharge (ESD) events may cause damage to electronic semiconductor components. ESD is a well-known problem in the operational environment of electronic circuit board assembly lines. In the past, ESD has been controlled by requiring human operators to wear grounded wrist straps. However, current automation trends have replaced human operators with robotic assembly equipment that uses insulative composite materials and ungrounded metal parts. Such equipment, including, for example, pick-and-place machines and IC testers, is difficult to analyze for susceptibility to ESD problems. It is quite time-consuming, if not altogether impossible, for engineers in factories to certify automated machines for ESD-free operation. The engineers must be able to detect occurrences of ESD events in order to apply the appropriate ESD mitigation methods to a given machine. This task is important because ESD events that take place in the context of automated machines are oftentimes of sufficient magnitude so as to damage one or more electronic components on a circuit board.
Presently-existing ESD event detectors, an example of which is disclosed in U.S. Pat. No. 4,631,473 issued to Masamitsu Honda on Dec. 23, 1986 and entitled, Transient Electromagnetic Field Detector", provide a momentary indication of the existence of an ESD event at the time that the event is actually taking place. This momentary indication takes the form of an audible beep or a flash of light emitted by an indicator lamp or LED. A human operator must be present at the time that an ESD event triggers the detector, or else information as to the occurrence of an ESD event is lost.
Prior-art ESD event detectors trigger an ESD indication whenever a received signal waveform has an amplitude above a predetermined threshold, irrespective of how many ESD events the received signal waveform actually represents. A single ESD event produces electromagnetic radiation which may be reflected by nearby metallic objects, resulting in the receipt of several signal peaks above a predetermined threshold. Unfortunately, existing ESD detectors are unable to distinguish a multi-peak waveform representing a single ESD event from a waveform that represents several ESD events. Moreover, existing ESD detectors provide no information about relative magnitudes of a plurality of ESD events, or the number of ESD events that occur within a given period of time. Such information is critical in determining the relative effectiveness of various proposed methods of ESD mitigation in environments where electronic devices are assembled and used.